Technical Field
This disclosure relates generally to control of the motion of camera components. More specifically, this disclosure relates to an actuator for a zoom lens in a miniature camera.
Description of the Related Art
Miniature cameras are typically used in mobile devices such as cellphones. In such devices, space is a premium and every effort is made to minimize the camera size. A zoom lens is a lens where the lens elements can be moved relative to one another to change the focal length of the lens. In doing so, this changes the field of view of the lens. In addition, such a lens is most typically required to adjust focus for different object distances. Many different configurations of zoom lens are possible. However, for a typical optical zoom lens, there are at least two lens groups that move independently of each other along the optical axis relative to the image sensor, but in a relational manner to each other. There are additionally typically further lens groups that remain stationary relative to the image sensor.
For large digital stills cameras (DSCs), such relational movements are often achieved by moving one intermediate component, such as a cylinder disposed around the lens that rotates about the optical axis. The cylinder may then has plural grooves on its inner surface to act as cam profiles, at least one groove for each moving lens group. In this way the rotation of the cylinder with a single actuator can achieve the controlled relational movement between different lens groups relative to the image sensor. Such mechanisms work well for DSCs, but are not suited to miniature cameras for several reasons. The most important reasons include manufacturing tolerances and associated clearances, and parasitic frictions and forces, and size constraints. For miniature cameras, the positional tolerances required for placing the lens groups are extremely tight; of the order of 10 um. This includes factors such as relative tilt between the lens groups, and the decenter relative to the nominal optical axis.
Unfortunately, for such precision mechanisms, manufacturing tolerances do not scale with size, and so a decenter error caused by a clearance between cam groove and pin follower on the lens group may be acceptable for a larger DSC, but unacceptable for a miniature camera.